Cardiovascular disease is the largest single cause of mortality in the general population. The incidence of CVD is far higher in patients with renal disease; the relative risk of CVD directly relates to age and the severity of renal disease. In chronic dialysis patients aged 45 years or younger, cardiac mortality is more than 100-fold greater than in the general population, and whilst this relative risk falls with age, it is still at least fivefold higher in elderly end-stage renal disease (ESRD) patients than in age matched general population (Foley, R., et al., Am. J. Kidney Dis. 32, 1998, S112-S119).
Monocytes play a crucial role in the development of atherosclerosis. They originate from the myeloid line of differentiating cells in the bone marrow. Blood monocytes are heterogeneous and may exist in a number of different phenotypic states. The main monocyte population in humans is CD14; CD62L+CCR2+ and is characterized by recruitment to inflammatory sites (NRI review) (see, for review, Ziegler-Heitbrock, L., J. Leucoc. Biol. 81, 2007, 584-592). The migration of monocytes is dependent on cognate interactions with endothelial cells. These interactions represent a multi-step process that depends on the expression of a number of molecules on the surface of circulating mononuclear cells.
The initial stages of monocyte recruitment to extravascular sites depends on the rolling of monocytes on endothelial cells. This process is facilitated by binding of (endothelial) cell surface proteins called selectins with glycoprotein ligands on the surface of circulating cells. One of the most important interactions in this group is between monocyte expressed p-selectin glycoprotein ligand-1 (PSGL-1/CD162) and endothelium expressed e-selectin and p-selectin; a recent study in an animal model of atherosclerosis confirmed that PSGL-1 was a major determinant for monocyte recruitment to sites of atherosclerosis (An et al).
Interactions between PSGL-1 and their counter-receptors allow leukocytes to bind weakly and roll on the surface of the vessel where they can sample the endothelial cell-surface micro-environment. Sequestered on the surface of endothelial cells, mainly through charge mediated interactions with cell surface proteoglycans, are small chemotactic cytokines called chemokines. Chemokines bind to (chemokine) receptors on the surface of the leukocyte to up-regulate expression of adhesion molecules on the surface of the mononuclear cells and to promote cyto-skeletal rearrangement.
The most important chemokine/receptor interaction for the firm adhesion of monocytes to endothelial cells is between MCP-1/CCL2 and CCR2 (see, for review, Barlic and Murphy, J. Leukoc. Biol. 82, 2007, 226-236). The level of expression of CCR2 on the surface of monocytes is an important determinant of the potential for monocyte recruitment (Weber C 1999). The direct effect of MCP-1/CCL2 on the adhesion of monocytes to endothelial cells is through up-regulation of integrin expression on the monocyte cell surface; these adhesion molecules bind to their counter-receptors, members of the super-immunoglobulin family, expressed on the surface of endothelial cells.
MCP-1/CCL2 ligation of CCR2 can rapidly promote conformational change in cell surface expressed Mac-1 (CD11b/CD18) a leukocyte β2-integrin; there is significant direct and circumstantial evidence for this integrin in the pathogenesis of CKD. There is both up-regulation of expression and a rapid change in conformation of the molecule to a high avidity state. These processes promote monocyte recruitment.
A further important pathway for the recruitment of monocytes in atherogenesis is through the chemokine fractalkine/CX3CL1, which is expressed by endothelial cells and it's ligand, CX3CR1, expressed on mononuclear cells including monocytes. CX3CL1 is an atypical, multimodular chemokine, which exists in membrane-tethered and soluble forms. The immobilized form consists of a chemokine domain anchored to the plasma membrane through an extended, mucin-like stalk, a transmembrane helix, and an intracellular domain. Full-length transmembrane CX3CL1 functions as an intercellular adhesion molecule, which mediates integrin-independent cell capture by binding to CX3CR1 on target cells. In atherosclerosis, both molecules are expressed on foam cells and coronary artery SMCs in both species, where the adhesion chemokine receptor CX3CR1 and its ligand CX3CL1 are up-regulated, promoting monocyte/macrophage capture and retention in the plaque (see, for review, Barlic and Murphy, J. Leukoc. Biol. 82, 2007, 226-236).
Recently it has been clearly shown that the relative contributions of CCR2 and CX3CR1 to leukocyte recruitment are similar, and knocking out both pathways has an additive effect on down-regulating mononuclear recruitment and the progression of atherosclerosis.
On recruitment to the arterial intima, the macrophage serves many functions related to atherosclerosis and its complications. Notably, it can secrete pro-inflammatory cytokines that amplify the local inflammatory response in the lesion, as well as reactive oxygen species. The activated mononuclear phagocyte plays a key role in the thrombotic complications of atherosclerosis by producing matrix metalloproteinases (MMPs) that can degrade extracellular matrix that lends strength to the plaque's fibrous cap.
When the plaque ruptures as a consequence, it permits the blood to contact another macrophage product, the potent pro-coagulant protein tissue factor. Eventually the macrophages congregate in a central core in the typical atherosclerotic plaque. Macrophages can die in this location, some by apoptosis, hence producing the so-called “necrotic core” of the atherosclerotic lesion.
The exact mechanisms relating CVD to the specific conditions of CHD patients are not completely elucidated, and thus potential therapeutic targets may remain. This is of great relevance in end-stage renal failure where a number of molecules of small and middle molecular weight may have a potential pathogenic role. Some of these molecules may activate monocytes, and are not removed by the current generation of dialysers that are in widespread routine use in clinical practice.
Conventionally, CHD patients are treated with high-flux dialyser membranes with a molecular weight cut-off of 15 to 20 kDa in the presence of whole blood. However, when used in convective therapies, namely hemofiltration and hemodiafiltration, proteins with higher mass may pass the high-flux dialyser membrane to some extent.
In order to improve efficiency, a new class of membranes that leak proteins below defined molecular weight cut offs (further referred to as “protein-leaking” membranes) have been developed for hemodialysis more recently. These membranes provide greater clearances of low molecular weight proteins and small protein-bound solutes than conventional high-flux dialysis membranes but at the cost of some albumin loss into the dialysate. While in a small number of clinical trials some improvements could be achieved using protein-leaking membranes, it remains unclear yet that routine use of protein-leaking membranes is warranted. It is also unclear whether protein-leaking membranes offer benefits beyond those obtained with conventional high-flux membranes, when the latter are used in convective therapies, such as hemofiltration and hemodiafiltration. Finally, the amount of albumin loss that can be tolerated by hemodialysis patients in a long-term therapy has yet to be determined (Ward, R. A., J. Am. Soc. Nephrol. 16, 2005, 2421-2430).
WO 2004/056460 discloses high cut-off (HCO) membranes which can be used in dialysers to eliminate circulating sepsis-associated inflammatory mediators more effectively than using conventional dialysis membranes. These high cut-off membranes, have much higher pore size than the above mentioned types. Pore sizes are in the range of 20 to 40 nm, three times larger than conventional (slightly) protein-leaking membranes and by a factor of four larger than the standard high flux membranes (12 nm and 9 nm, respectively). The high cut-off membranes have a molecular weight cut-off, measured in the presence of whole blood, of 45 kDa whereas the cut-off of the other types of membranes usually does not exceed 20 kDa (see also above). This cut-off measured in blood clearly indicates that substances, like smaller proteins, with a molecular weight from 20 to 45 kDa can penetrate these high cut-off membranes to a significant degree.
Recently, a remarkable clearance of interleukin-6 (IL-6) with high cut-off treatments leading to a significant decrease in circulating IL-6 levels in septic patients suffering from acute renal failure was demonstrated (Morgera, S., et al., Intensive Care Med. 29, 2003, 1989-1995). Furthermore, such treatment led to a restoration of immunoresponsiveness of blood cells in those patients (Morgera S., et al., Nephrol. Dial. Transplant. 18, 2003, 2570-2576). A study where patients were randomly allocated to high cut-off, continuous veno-venous hemofiltration (CVVH) or hemodialysis (CVVHD) showed that convection and diffusion did not exhibit the expected difference in terms of clearance of middle-molecular-weight proteins, whereas using diffusion instead of convection significantly reduces the loss of albumin while maintaining good cytokine clearance rates. In CVVHD mode, a maximum albumin loss of 950 mg per hour in patients treated with the HCO membrane was reported (Morgera S., et al., Am. J. Kidney Dis. 43, 2004, 444-453).
EP 1 852 136 A1 discloses a method of reducing blood free light chain concentration in a subject suffering from multiple myeloma, wherein the subject's blood is subjected to hemodialysis, hemodiafiltration or hemofiltration by using a HCO dialysis membrane to reduce blood free light chain concentration in the patient. In this way, chronic renal failure is prevented or slowed.
The applicants have now found that such membranes can also be used to effectively treat end stage renal failure (ESRD) patients.